In work with hyperkinetic children, we have found that stimulant dose/response studies of event related potentials (ERP) disclose effects of age and of selective attention that would otherwise have been obscured. By varying stimulant dose, age and task demand the serial processes revealed by the ERP can be further separated and disassociated. The use of so many variables poses special problems. Nevertheless, carefully varying these three major factors (age, dose and task demand) allows us to learn more about the effects of any one of these factors than would be possible if that single factor was the only variable. By applying this approach to elderly subjects, we hope to discover if selective attention changes with advancing years and how responses to stimulants are manifested in the aged. These are important questions in themselves, but, in addition, we hope this new population will provide a further disassociation of the components involved in the serial selective processing of sensory data and perhaps provide new clues as to the data handling processes and their neural substrates.